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AiiT. IV. — On the Granite of Aberdeenshire, and on the 

 Identity of certain Varieties of Granite, with other Rocks 

 appertaining to the Trap Family — By J. Mac Cul- 



'' LOCH, M.D., F.R.S. Communicated by the Author. 



It is well known to those who are conversant ^with rocks, that 

 many members of the trap family, including under that term all 

 the unstratified rocks which lie above the secondary as well as 

 the primary strata, bear a striking resemblance in their mineral 

 composition and general aspect, to some of the varieties of 

 granite ; there being comprised under this denomination, all 

 the unstratified rocks which are inferior, not only to the se- 

 condary, but to the primary strata. A very remarkable instance 

 of this resemblance, is pointed out in the article which relates 

 to the Isle of Sky, in my work on the Western Islands of 

 Scotland ; and similar examples, if less striking, may be seen 

 in many parts of that country, so fertile in all the interesting 

 appearances which are found in the rocks of this multifarious 

 family. The important views that may be deduced from these 

 facts, will be considered hereafter ; it being the primary object 

 of this paper, to confirm this important analogy by evidence 

 from a different source, but of the same nature, derived from 

 the existence of those rocks which form some of the most 

 common and conspicuous varieties of the trap family, not only 

 in the situation occupied by granite, but connected with the 

 most authentic masses of that substance by a bond of mutual 

 and imperceptible transition. 



Those who are acquainted with Scotland, know that granite 

 occupies an extensive space in Aberdeenshire ; and that where 

 it does not appear at the surface, it is covered, and often to a 

 very inconsiderable depth, by different members, both of the 

 primary and secondary strata. 



Among these, gneiss is the prevailing rock. In some situa- 

 tions, it forms mountains of considerable elevation, such as Noath 

 and Coreen ; but, towards the eastern side of the country, it is 

 found at a general, but irregular low level ; like the granite, 



